A solar cell made from polycrystalline silicon, microcrystalline silicon or amorphous silicon is well known. Especially, with respect to resource consumption and from the viewpoint that a reduction in costs and an increase in efficiency is desirable, the focus has been on a photoelectric conversion device having a laminated structure composed of microcrystalline silicon or amorphous silicon thin films.
Generally, a photoelectric conversion device is produced by laminating, on the insulating surface of a substrate, a first electrode, one or more semiconductor thin film photoelectric conversion cells, and a second electrode, in the stated order. The individual photoelectric conversion units for the device are formed by laminating a p-type layer, an i-type layer and an n-type layer, beginning on the light incidence side. A well known method for increasing the conversion efficiency of the photoelectric conversion device is the stacking of two or more types of photoelectric conversion cells in the direction of the incidence of light. For the photoelectric conversion device, a first photoelectric conversion unit, which includes a photoelectric conversion layer having a large bandgap, is arranged on the light incidence side, and behind this unit, a second photoelectric conversion unit is arranged that includes a photoelectric conversion layer having a bandgap narrower than that of the first photoelectric conversion unit. With this arrangement, photoelectric conversion can be performed for a wide wavelength range of incident light, and an overall increase in the conversion efficiency is obtained for the device. For example, a structure is well known wherein an amorphous silicon (a-Si) photoelectric conversion unit is employed as a top cell and a microcrystalline silicon (μc-Si) photoelectric conversion unit is employed as a bottom cell. Above all, attention has been drawn to a structure wherein amorphous silicon and microcrystalline silicon are deposited in the stated order, on a translucent substrate, and light is permitted to enter and impinge on the substrate face, and with this structure, an integrated large-area module can be easily provided and the size of the area of the translucent substrate that does not contribute to photoelectric conversion can be reduced.
A technology is also disclosed whereby a microcrystalline silicon thin film containing impurities and an amorphous silicon thin film, which also contains impurities, are laminated, in order, to reduce the grain boundary of an electricity-generating layer or an intercrystalline defect, and to increase photoelectric conversion efficiency. Especially disclosed are the deposition of a p-type microcrystalline thin film and a p-type amorphous silicon thin film on a back-contact electrode, which is located on the side opposite the light incidence side, and the application of amorphous silicon or amorphous carbide silicon for the p-type amorphous silicon thin film (see, for example, patent literature 1).